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Chapter 5: Research on Long-Term Operation of ARGG Units and Technical Countermeasures. In recent years, thanks to the continuous improvement in design standards, process measures, and equipment reliability, the domestic oil refining industry has gradually managed to achieve long-term operation of its units; among these, achieving a maintenance cycle of \"two or three years\" for catalytic units is particularly representative and significant. Achieving long-term operation of the device is a complex systematic task that requires continuous summarization, exploration, and improvement. At the same time, ensuring long-term operation of the device is also the best and most effective measure for saving energy and reducing consumption. Since the commissioning of one ARGG unit at Daqing Refining & Chemical Company in September 2003, problems such as scaling on the moving and stationary blades of the turbines and coking in the slurry system have persisted, preventing the unit from achieving a relatively stable operating environment. The best operating record is 17 months of continuous operation, after which shutdown for maintenance was necessary due to the failure of the heavy oil slide valve, which allowed large amounts of catalyst to enter the bottom of the distillation tower. According to preliminary estimates, each maintenance cycle for a 1 million tons per year ARGG unit requires costs of around 8–10 million yuan, with a duration of approximately 15 days. These figures do not include losses related to materials used during startup and shutdown, nor the inability to complete planned processing tasks. Achieving long-term operation of an ARGG unit is a requirement for continuously improving management levels, and it is also a prerequisite and foundation for enhancing the unit’s energy efficiency and productivity. To this end, we have carried out extensive exploration and experimentation, and to date substantial progress has been made in addressing issues such as fouling of smoke machines, which lays a solid foundation for ensuring the long-term operation of these devices in the future. 5.1 Long-term operation status of CNPC’s main units: In recent years, thanks to the continuous improvement in management standards, CNPC’s main refining units have broken free from a state of stagnation, and their operation cycles have been significantly extended. 48 main units have achieved a maintenance cycle of more than once every three years; 19 of these units even have a maintenance cycle of more than once every four years. Among them, catalytic cracking units are the most representative in terms of achieving long operation cycles. Catalytic cracking units have always been the key production units for oil refineries to achieve economic efficiency. With rising raw material prices and an increasingly internationalized product market, long operation cycles have become a focus for oil refineries aiming to maximize their profitability. The typical service life of catalytic cracking units abroad is 3 to 5 years, with Sinopec achieving the best result of around 4 years (1,450 days). Meanwhile, PetroChina’s companies such as Daqing Petrochemical and Harbin Refinery have already managed to achieve a maintenance cycle of once every three years for their catalytic units. Among the five production units at Refinery No. 1 of Daqing Refining & Chemical Company (atmospheric and vacuum distillation, gas separation, acidic water treatment, reforming, and one ARGG unit), except for the 1 million tons per year ARGG unit, the other four units have already reached a level that allows for maintenance cycles of over three years. However, this still falls far short of the standards of other refining and chemical companies both domestically and internationally, as well as those within CNPC. Therefore, it is urgent to ensure long-term operation of our company’s ARGG unit, and there is significant potential for improvement in this regard. The main factors currently affecting the long-term operation of an ARGG unit include fouling of the smoke extractor and coking in the slurry system. 5.2 Scaling issues in the flue gas turbines of CNPC’s refining and chemical enterprises: Since 2004, due to an increase in the renovation and expansion of catalytic units in these enterprises, adjustments to production plans, and the adoption of new catalysts for increasing propylene production, the propylene yield and oil refining capacity have been continuously improved. As a result, more than 20 catalytic units at companies such as Daqing Refining & Chemical, Daqing Petrochemical, Dalian Petrochemical, and Jinzhou Petrochemical have experienced scaling or coking problems in their flue gas turbines, requiring frequent repairs as a consequence of these issues. Although the causes of fouling or coking in the flue gas turbines of various refining and petrochemical companies vary, the increasing severity of this problem poses a serious threat to the safe operation of these facilities, as well as to energy recovery and long-term operational continuity. To this end, CNPC’s Refining and Sales Division held several specialized seminars to conduct thorough analysis and gather ideas, and issued the \"Guidelines for Preventing Scaling in Flue Gas Turbines\" and the \"Technical Guidelines for the Long-Term Operation Management of Flue Gas Turbines\" as a guide. Through nearly four years of unremitting efforts, significant progress has been made in addressing the fouling problem of the flue gas fan in one of the ARGG units at Daqing Refining and Chemical Company. Since it began operating in September 2007, the flue gas fan has remained in stable operation. 5.2.1 Analysis of the operation status of the exhaust fan in one set of ARGG units at Daqing Refining & Chemical Company. Since the operation of this set of ARGG units began in September 2003, the exhaust fans have also suffered from scaling problems, which required repeated removal and repair. Based on the quality of the exhaust fans’ operation, it can be roughly divided into three stages and four periods; the specific details are shown in Tables 5-1 and 5-2. Table 5-1: Statistics on Fan Failures of Unit 1 ARGG in Daqing Refining & Chemical Complex from 2005 to 2008
Date, Vibration Levels Before and After the Fan, Scaling Locations, Wear Conditions, Remarks
September 2003 – April 2004: Normal, Normal. The fan operated properly using CC-20DF catalysts; no scaling occurred.
May 2004 – October 2004: Normal, Normal. The fan operated properly using CC-20DF catalysts; no scaling occurred.
October 2004 – March 2005: Normal, Normal. CC-20DF catalysts were gradually replaced with CA2000 or RAG-6 catalysts, and production was carried out according to the gas production plan. On March 7, the vibration level before the fan increased from 30 μm to 40 μm, while that after the fan rose from 60 μm to 76 μm. Scaling occurred on the drive belt and blades; the tips of the blades were abraded, and balance adjustment was performed. From March 8 to 10, the unit was shut down for emergency repairs, and a spare rotor was installed. On April 4, the vibration level rose to 79 μm; scaling persisted on the drive belt and blades, and erosion and wear were observed 2 cm from the top edges of the blades where gas entered and exited. Laser cladding and re-coating were carried out. From April 4 to 6, emergency repairs were conducted again, with a spare rotor installed. On May 3, the vibration level after the fan increased to 92 μm; scaling occurred on the drive belt and blades, as well as erosion and wear at the edges where gas entered and exited. Erosion also occurred on the tenon teeth of the rotor. Laser cladding and re-coating were performed. From May 3 to 5, the unit was shut down for emergency repairs; the steam supply point for cooling the fan was moved closer to the turbine outlet, and a spare rotor was installed. On May 23, the back vibration rose to 87.5 μm; fouling occurred on the moving blades, and erosion was seen at the inlet and outlet edges of these blades. The plant was shut down for emergency repairs from May 23 to 25. A spare rotor was replaced. On June 21, the vibration level rose to 95 μm; there was scaling on the shrouds and vanes, as well as slight wear at the tips of the vanes. The plant was shut down for emergency repairs from 11:30 on June 21 to 11:45 on June 23. Replacement of spare rotor: On July 11, the vibration level behind the flue gas turbine suddenly rose to 108 μm; reducing the butterfly valve to 30% reduced this value to 70 μm. On July 6, an additive to increase propylene production was added. On July 25, severe scaling occurred on the surrounding belt, and the tops of the rotor blades were severely worn and had irregular shapes; there was also scaling on the rotor blades, with severe erosion and wear at their inlet and outlet edges. From July 25 to 27, the unit was shut down for emergency repairs, and a spare rotor was installed. On August 8, the vibration levels before and after the turbine rose to 160 μm; there was severe scaling on the surrounding belt and on the rotor blades, as well as wear on their tops. One of the rotor blades broke in the middle. Even after cutting off the flue gas flow, the vibration level did not decrease, so the unit was shut down urgently and a spare rotor was installed. On September 12, the vibration levels before and after the flue gas turbine suddenly rose to 160 μm; the turbine vibrated intensely. The tops of the rotor blades were worn, and one of them broke in the middle. A spare rotor was installed. On September 26, there was slight scaling on the rotor blades, with a layer of scale about 2 mm thick at their roots; the scaling on the surrounding belt was also about 2 mm thick. The guide cone was removed to clean the scale, after which it was reinstalled. On October 4, no scale was found on the surrounding belt, and there were no lump-shaped deposits on the rotor blades; however, there were erosion pits in the middle of the rotor blades. The guide cone was removed to clean the scale, after which it was reinstalled. On October 11 and 16, the vibration level in front of the flue gas turbine was 54 μm. The flue gas flow was cut off, the unit ran idle for 4 hours, and then it was put back into operation. On October 29, there was slight scaling on the rotor blades, with erosion pits in their middle and tops. From October 29 to November 3, emergency repairs were carried out on the unit; there was still slight scaling on the rotor blades, along with erosion pits in their middle and tops. The spare rotor was replaced and put into operation on November 6. From November 2005 to June 2006, the flue gas turbine operated normally without any signs of scaling. On June 9, the vibration level of the flue gas turbine was 70 μm; scaling occurred on the drive belt and moving blades, so the spare rotor was replaced again. On July 17, the vibration level was 65 μm; scaling still existed on the drive belt and moving blades, prompting another replacement of the spare rotor. On August 4, the vibration level was 70 μm, with scaling on the drive belt and moving blades. On August 14, the unit was shut down for maintenance. From September 2006 to April 2007, the flue gas turbine operated normally without scaling. On April 16, the vibration level increased to 56 μm; there was slight scaling on the moving and stationary blades. The main unit was started at 6:45 on the 20th, and the two units were switched over at 7:00. On June 17, at 15:06, the vibration level rose to 60 μm; there was catalyst scaling at the junction of the moving blades and the drive belt, severe wear at the tips of the moving blades, and serious erosion pits at the blade corners. On June 22, the main fan was started, and the flue gas turbine was put back into operation at 20:00. On August 1, the vibration levels before and after the flue gas turbine increased, to 42 μm respectively; hard scale deposits were present on the moving blades, while there was significant scaling on the liner rings and drive belt. There was wear at the tips of the blades and erosion pits at their roots. The scale was removed from the drive belt and blades before they were reinstalled. From September 2007 to May 2008, maintenance was carried out on August 14, during which another spare rotor was replaced. Table 5-2 shows the operating status of the flue gas turbine in an ARGG unit from 2003 to 2008. Time | Operating Status | Remarks: September 2003 – October 2004: First phase – Stable operation; the turbine operated normally. October 2004 – November 2005: Second phase – Frequent failures; scaling occurred frequently after the use of a catalyst to increase propylene production. November 2005 – September 2007: Period of efforts to prevent scaling; as scaling began to occur, the frequency of turbine failures decreased from once per month to once every two months, indicating a slowdown in the scaling trend. September 2007 – May 2008: Third phase – Relatively stable period; the turbine has been operating steadily for 9 months now. 5.2.2 Brief overview of turbine scaling: As can be seen from the table, during the first phase, from when the unit first started operating in September 2003 until October 2004, the ARGG unit used the CC-20DF catalyst according to the specified catalytic process. During this time, the turbine operated smoothly. Although in March 2004, the unit experienced issues due to power fluctuations, resulting in significant loss of catalyst, and production had to be maintained by temporarily adding balancing agents, approximately 150 tons of catalyst were lost by the time of maintenance. However, upon disassembling the turbine for inspection, it was found that the moving and stationary blades as well as their coatings were intact, with no signs of scaling. This indicates that catalyst loss at this stage is not the cause of soot burner fouling. In the second and third phases, from October 2004 to the present, to meet the needs of polypropylene production and in accordance with the adjustments to the company’s production plan, the ARGG unit began operating under a gas-production mode. The catalyst was gradually replaced from CC-20DF with a catalyst designed to increase polypropylene production, with CA2000 or RAG-6 being used at various times. At the end of February 2005, the vibration of the smoke extractor increased from around 30 μm to around 45 μm; after observing its operation for a week, the vibration suddenly rose to 80 μm, reaching the lower limit of the alarm threshold. Following the shutdown for disassembly inspection, it was found that the rotor blades, shrouds, and guide cones of the smoke turbine were severely fouled, while the blade tips were abraded and the outlet edges were eroded, as shown in Figures 5.1 and 5.2 below. Figure 5.1: Scaling and erosion conditions on the moving blades. Figure 5.2: Scale samples from the surrounding areas. Figure 5.3: Scale samples from the flue gas turbine along with analysis of the catalyst composition. In order to address the issue of scaling in the flue gas turbine more promptly, the Technology Department of Daqing Refining & Chemical Company commissioned the Petroleum Processing Science Research Institute to conduct a thorough analysis of these scale samples (samples collected on March 8, 2005). The specific data are as follows: Table 5-3: Analysis and evaluation report from the Petroleum Processing Science Research Institute. Commissioning party: Daqing Refining & Chemical Branch. Contact number: … Sample name: Cracking catalyst. Date of sample submission: March 10, 2005. Date of report issuance: March 22, 2005. Analysis items: Element contents. Sample number: Analysis of inorganic elements/% Al2O3 Na2O Fe Ni V Ca. Daqing regenerated agent: 48.6 0.3 0.3 0.47